This invention relates to magneto ignition systems for use in chain saws, string trimmers, or the like, and, in particular, to improved magnetic structure for use in such systems.
Various ignition systems are known and disclosed in such patents as U.S. Pat. Nos. 4,120,277; 4,169,446; and 4,194,482, the foregoing patents being hereby incorporated herein by reference. These ignition systems are typically characterized by magnetic circuitry which includes a permanent magnet embedded in the periphery of a rotor or flywheel, the magnet acting in cooperation with a coil or coils disposed adjacent the flywheel such that rapid flux changes are induced within the coil each time the embedded magnet passes the coil. A permeable core structure is at least partially disposed within the coil to enhance the flux concentration therein. The coil is connected to ignition circuitry whereby the voltages induced in the coil are applied to the circuitry to effect actuation of a conventional ionization discharge device such as a spark plug.
The foregoing ignition systems are typically incorporated in hand held devices such as chain saws, string trimmers, lawn mowers, edgers, hedge trimmers, et al. Accordingly, these devices should be as light as possible to enhance the portability thereof. In known structures of the above type, magnets of a predetermined size have been employed together with associated pole piece structure where the size of the magnet has been determined by the amount of flux needed to generate appropriate flux changes in the coil of the ignition circuit.
In accordance with one object of this invention, it has been determined that the magnetic structure can be reduced in size or weight by twenty to twenty-five percent and, yet due to the improved magntic structure employed in the present invention, the requisite levels of flux are produced in the coil of the ignition circuit. This reduction in the weight of the magnet structure translates into enhanced portability of a chain saw or the like. Moreover, magnetic coupling between the improved magnetic structure of the present invention and the permeable core of the coil is enhanced thus resulting in a reduction in leakage flux between these elements as compared with prior art magnetic structures used in ignition systems and the like.
Typically, a plurality of fins are disposed around the flywheel periphery for cooling purposes where some of these fins are disposed above the embedded magnetic structure. However, due to the larger size of the magnetic structure employed heretofore, the size of the fins disposed above the magnetic structure has been rather small.
Accordingly, it is a further object of this invention to provide an improved magnetic structure of the above type wherein, due to the decreased size of the structure employed, larger fins may be employed on the flywheel in the area occupied by the magnetic structure to thus enhance the cooling effected by those fins and the overall cooling effected by the flywheel.
It is a further object of this invention to provide improved magnetic structures of the above type in conjunction with current sheet inductor ignition systems, as will be described in more detail hereinafter.
It is another object to employ the above improved magnetic structure in chain saws, string trimmers and the like.
Other objects and advantages of this invention will be apparent from a reading of the following specification and claims taken with the drawing.